One big difference between US submarines and former USSR and Russian submarines is that when you look at a US submarine hull, you are looking at the pressure hull. With few exceptions, the Soviet/Russian hulls are double hulled, with the inner hull being the thick pressure hull. The submarines' outer panel have limber (free flood) holes to flood the space between the inner and outer hulls. There are visible on the outer Alfa hull (in my B&W closeups) faint join areas, in addition to limber holes. If I was going to model the weld lines, I would use subtle variations in paint shades to delineate them. Take a look at the Alfa photos in the 2 links. You can see how subtle the lines are (almost non-existent to the eye). The welds were very tight in the outer hull, and the hull was as smooth as possible due to the Alfa's speed. Scroll down on the second link for more dry dock photos to illustrate the point.
Alfa design goes back to the late 1950's. To their credit, this design included the titanium hull, a small crew with a great deal of automation, and a liquid metal (lead-bismuth) OK-550 reactor, which had greater power density than the pressurized water reactors. This combination of streamlining and reactor design allowed the submarine to reach great speeds of around 40 knots. But, at high speed, the Alfa was extremely noisy and could be tracked by SOSUS arrays from thousands of miles away. The liquid metal reactor was also problematic; it had to be kept "warm" (>50C) or the metal would freeze in the reactor core. The original hull, K-64, suffered such an accident where the metal solidified shortly after going into service. She was cut in half and the front half used for training. Another reactor in K-123 had a liquid metal spill of two tons into the reactor compartment. In the end, these were expensive to build, expensive to maintain, and had more than one serious reactor incident in the six hulls built.
Alfa in dry dock
Several photos-scroll down